This invention relates to a transfer machine for transferring inspected elements such as semiconductor wafers from a start point to an end point in a surface inspection apparatus for inspecting undesired particles and abnormalities such as cracks, dirt, foulness or the like on a surface of the semiconductor wafers.
In a conventional surface inspection apparatus, a laser beam is radiated onto a surface of a semiconductor wafer so that the reflected laser beam can be detected thereby to inspect undesired particles and abnormalities such as cracks, dirt, foulness or the like on the surface of the semiconductor wafer. A plurality of wafers are stored in a storage housing such as a carrier or cassette and then taken out thereof one by one in order. Each wafer is transferred to a measuring stage in the surface inspection apparatus while it is tentatively held by a chuck in a fixed condition. At that time, the wafers move at a single grade level along a horizontal plane. After they are inspected at the measuring stage, they are further transferred and then stored in the other storage housing one by one in order.
In general, such a transfer machine must be enlarged in size as wafer sizes become large. Thus, installation space problems occur in practice. In order to solve such problems, various type machines transfer have been proposed.
In the prior art transfer machines, however, the wafers move only at a single grade level along a horizontal plane from one storage housing to the other storage housing. It is very difficult to miniaturize a transfer machine. In fact, effective floor spaces for transfer machines increase because wafer sizes have recently become large.